Idiom: (to) drop by
Definition:
to pay a short, often unannounced visit
Examples:
1) If we have time before the movie, let’s drop by my house.
2) “Hi, I was in the neighborhood and I thought I’d drop by”.
中文解释：http://www.youzienglish.com/main/idiom_of_the_day/to_drop_by/cn/
